I have been trying to synthesize hematite iron oxide via a hydrothermal and sol gel method. Through a hydrothermal synthesis, I could get the crystalline Fe2O3 after calcination in N2 atm. (inert) at 500 oC. But why I can't get it in the same calcination process when the Fe2O3 was synthesized via sol gel? What is the real driving forces to get crystalline metal oxides through calcination in N2 atm?
There is a huge amount of literature, including books, on the synthesis of iron oxides (Schwertmann, Cornell, 2000: Iron Oxides in the Laboratory: Preparation and Characterization). Based on what I know about the issue, calcination in an inert atmosphere seems to me to be an unnecessary step in this case. Possible further oxidation of Fe(II) residues by atmospheric oxygen will be more beneficial. Fe2O3, i.e. hematite will be formed from (meta)stable phases, such as ferrihydrite, etc., especially in the sol-gel method. The anions present also have an influence.
Dalibor Matýsek Thank you so much for your answer.
In my case, I am looking for a method where I could get Fe2O3 via sol-gel without calcining it through any oxidative atmosphere. So will it be possible? I found a paper that done so but they synthesis their Fe2O3 through hydrothermal (attached).
and may I ask for further elaboration on the influence of the anions in the sol-gel process? or is there any useful reference I could access related to it? Once again thank you so much in advance.
My opinion is that it probably won't be possible in an aqueous environment at room temperature. It's about hydration/dehydration energy. Although ferrihydrite is limited in stability, its spontaneous dehydration is a rather slow process. But it works in an autoclave, in hydrothermal conditions, approx. 120oC and more.
Article Hydrothermal synthesis of hematite (α-Fe2O3) nanoparticle fo...
This isn't exactly a sol-gel method either:
Article Room Temperature Synthesis of Crystalline α -Fe2O...
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